Automatic retarder system for a railroad classification yard



Aug. 6, 1963 A. M. CRAWFORD ETAL 3,100,098

AUTOMATIC RETAROER SYSTEM FOR A RAILROAD CLASSIFICATION TARD Filed July l2, 1962 AJI sa 'i 9 5' A TTORNEYS.

United States Patent O 3,100,098 AUTGMATIC RETARDER SYSTEM FOR A RAIL- RAD CLASSWlCATlUN Y Archibald M. Crawford, 6427 Kentucky Ave., Pittsburgh 6, Pa.; Kenneth M. Lockerby, 1900 Pennsylvania Blvd., Philadelphia 3, la.; and Robert H. Brown, Devonwood Road, Wayne, Pa.

Filed duly 12, 1962, Ser. No. 212,179 4 Claims. (Cl. 246-182) This `application is a continuation-impart of our copending patent application, Serial No. 727,694, filed April l0, 1958, entitled Automatic Retarder System for a Railroad Classification Yard.

The present invention relates to railroad freight classification yards. More particularly, the invention concerns a retarder system for effecting, in response to track-fill information automatically sensed, automatic control of the final `coupling speed of railroad cars in a classification yard. For description of an automatic system for sensing track fill, see US. Patent 2,930,888, granted to us March 29, 1960, on our co-pending application Serial No. 569,648, filed March 5, 1956.

ln the routing and delivering of railroad freight, freight trains are made up at different points and include, o-f course, freight cars having various destinations. Such trains are later routed to a classification yard which acts as a clearing house. Its function is comparable to that of a big city post oce where letters picked up from many different towns are sorted into separate groups for direct dispatch to their addresses. In the case of freight trains, to avoid having to sort and re-sort the cars several times on route, the freight trains are sent to a classification yard -ivhere the cars are classified according to their destinations.

After arriving at the classification yard, coupled cars are pushed up an' elevated hump where the are uncoupled or cut. From the hump, the cut cars coast down into one of a number of classification tracks, with cars for the same destination being directed into the same classification track. As each cut car starts down grade, its route is set up by switches that direct it into the proper path. Braking devices, known as retarders, are provided along the track. These retarders straddle the tracks and squeeze the wheels to slow the car a controlled amount so that it will later come to rest in a desired position. After all the cars for the same destination are assembled, they are made up into new trains and sen-t on their way.

lt is an object of this invention to provide means for continuously sensing the condition of a classification track as to its occupancy by railroad cars, or the location of cars therein, and to utilize the sensed information to automatically control the speed of subsequent railroad cars routed toV such classification track.

It is another object of this invention to ascertain whether or not a railroad car moving along -a classification track has at least exceeded la predetermined minimum speed.

It is an object of this invention to accomplish the aforesaid objects automatically and without lany manual manipulation.

Further objects and .advantages of the invention will become apparent from the detailed description which follows, in which reference is made to the accompanying single sheet of drawing showing a diagrammatic view of one specific form of apparatus constructed in accordance with the invention.

In describing the preferred embodiment of the invention illustrated in the drawing, specific terminology will be resorted to vfor the sake of clarity. However, it is not our intention to be limited to the specific terms so lCe elected, and it is to be understood that each specific term includes all technical equivalents which oper-ate in a similar manner to accomplish a similar purpose..

rBurning now to the specific embodiment of the invention selected for illustration in the drawing, there is shown an automatic retarder system including a retarder 1, retarder control means 2, sensing mechanism 3, including electronic detector unts A, B, C, and D, and slow cut mechanism 4 for determining whether the preceding railroad car is moving .at iat least a minimum satisfactory speed. A single classification track 11 is shown having the two rails 12 and 13. In the classification yard, there will -be a number of classification tracks such as track 11, but only one is illustrated. The track 11, while electrically continuous may :be considered for the purpose of the present application as divided into -four sections a, b, c, and d, the section limits being indicated by the dot-ted lines 14, 15, 16, 17, `and 18. Classification track 11 is electrically isolated from the remainder of the classification yard by insulated joints 19 and 20.

Detector unit A is adjusted so that it responds to the condition of that portion of classication track 11 identified as track section a, i.e., it detects the presence of a car or cars in track section a; detector B detects the presence of a car or cars in track section b; detector C detects the presence of a car or cars in tra-ck section c; and detector D detects the presence of a car or cars in track section d.

An oscillator 21 is provided (which may be a known type ofsine wave oscillator) having poor voltage regulation as one of its characteristics. If an oscillator having good voltage regulation be used, a series resistor is incorpora-ted in the oscillator circuit to provide a high impedance source, thereby to provide the poor voltage regulation required yfor the practice of lt-he present invention. Connected across the oscillator 21 is an amplier 22 the output of which is applied, as by conductors 23, 24, across rails 12 and 13 yat the entry point 18 to the track 11. The output of amplifier 22 is also applied across the parallel-connected primary windings 25 of the four transformers 26.

The secondary winding 27 of each of the transformers 26 is connected into -an lassociated detector or sensing circuit, each of which is shown to include a gas t-ube 28 having an anode 31, a cathode 32, a control grid 33, a screen ygrid 34, and a filament 35.

The control grid circuit of each tube 28 receives energy from the track circuit. The tr-ack circuit may be considered as including rails 12, 13, oscillator 21, amplifier 22, conductor 23, 24, and the primary winding 25 of each transformer 26. Each control grid circuit includes the secondary winding 27, a series rectifier 36, and a capacitor 37 and resistor 38 connected in parallel across the winding 27 Iand the series rectifier 36. Also included in the control grid circuit of unit A is a series resistor 41a and a variable bias resistor 42a having a capacitor 43 connected thereacross.

In general, like numbers are used to designate like parts in the sensing units A, B, C, land D. However, the bias resistors are differently adjusted and are designated 42a, 4211, 42e, and 42d, respectively, for units A, B, C, and D. Similarly, the control grid resistors are designated 41a, 41h, 41e, and 41d, respectively.

The A.-C. voltage `applied to the rails by amplifier 22 causes `a rectified voltage to be applied to the control grid 33 of each tube 28. This `applied voltage is opposed by the negative bias voltage supplied by the bias current flowing through the bias resistors 42a, 42b, 42C, 42d, Aand is dependent on the position of the tap.

In each of the sensing units, the bias current is provided by a similar circuit. The bias circuit of unit A, for example, can be traced from terminal 44 of A.-C. line 4S Patented Aug. 6, i963 through terminal 46, wire 47, rectified 4S, -resistor S1, the paralleled resistor 42a and capacitor 43, wire 52 and terminal 53 back to line 45 at terminal 54.

The anode-'cathode or plate circuit for each tube 28 includes the anode 31, resistor 55, a relay (identied as a', b', c', and d', in detector units A, B, C, and D, respectivley) a capacitor 57 connected across each relay a', b', c', d', the secondary winding 58 of a transformer 61 (having its prima-ry winding 62 connected across A.C. line 45), 4a capacitor 63 in parallel with secondary windings 58, and the cathode 32. It will `be seen, then, the anode 31 of each tube'is supplied with an A.C. plate voltage from the transformer 61.

Relays a', b', c', and d control the indicating lamp circuits, which include lamps sa-68d. Relays a', b', c', and d also control follower relay circuits, each having a Adifferent time delay, for controlling, through computer 80, the ret-arder control means 2.

The mode of operation of the sensing units A, B, C, and D may best be understood by assuming illustrative values for the circuit selected for illustration in the drawing. Tubes 28 fire when the voltages on the plate and on the control grid 33 are positive. It is desired that the voltage on the grid of each tube be positive when there are no cars on track 11. The output voltage of the oscillator amplifier 22 when there are no Icars on track 11 may be assumed to be 3.0 volts (at 100 cycles) as measured across the rails 12, 13, at about the point indicated by the dotted line 18. This 3.0 volts also appears across each of the transformer windings 2S.

When there is a car on the track l1, the voltage appearing across windings 25 Varies with the .position of the car on the track. When the car is lat dotted line 18, which may be considered the entrance to track 11, the voltage -across windings 25 is zero since the car shorts the rails at the point of application of the voltage. \Vhen the car arrives at dotted line 17, the voltage Iacross the rails at entry point 18 and -across windings 25 is 0.5 volt, since the rails of section d have resistance. When the car is at dotted line 16, the voltage at 1S is 1.0 volt; when the car is at dotted line 15, the voltage at 18 is 1.5 volts; Iand when the car is at dotted line 14, the Voltage lat 18 is 2.1 volts. Bias resistor 42a may be .assumed to be set to provide 4minus 2.0 volts on the grid of the tube of unit A in the absence of any track voltage; bias resistor 42h is set to provide 1.5 volts, 42C 1.0 volt, and 42d 0.5 volt. Thus, with no car on 4track 11, the grid voltage (between grid 33 and cathode 32) of detector unit A is 1.0 volt, (3.0 volts track voltage minus 2.0 volts bias voltage); the grid voltage of detector unit B is 1.5 volts; of detector unit C is 2.0 volts; 'and of detector unit D lis 2.5 volts. Thus, lwith no car on track 11, all the control grids 33 are positive, all the tubes 2S are tiring on the positive cycles of the A.C. plate Voltage, and all the la-mps 68a68d are extinguished.

When a railroad car lirst rolls into track 11, its wheels short circuit the rails 12, 13, at entry point 18, and the voltage across windings 25 is reduced to zero. The control grids of tubes 28 then have impressed thereon only the negative bias voltage provided by the lbias circuits, as picked off by resistors 42a, 42h, 42e, land 42d. Under this condition, all the tubes 28 cease tiring when the A.C. plate voltage drops to or toward Zero, and the relays a to d are each de-energized.

As the car moves through track section d, the voltage `across the rails at entry point 18 increases; Iand when the car passes the point identiiied as 17, the voltage across windings 25' becomes 0.5 volt, sullicient to overcome the 0.5 volt negative bias to resistor 42d of unit D. This causes tube 28 of detector unit D to lire and energizes control relay d'.

As the car continues to roll drown track 11 and passes beyond point `16, the track voltage at entry point 1S rises suiciently to allow tube 28 of unit`C to tire; and when the car passes beyond track limit 15, tube 28 of unit B lires. It will be assumed that the car stops in track section a. It so, the voltage at entry point 18 fails to rise to 2.0 volts, and tu'be 28 of detector unit A remains negatively biased and is prevented from re-iring. Control relay a' is therefore prevented from re-energizing.

It will be assumed that succeeding cars completely till up track section a. Thereafter, the iirst car to stop in track section b prevents the track voltage tot entry point 18 from rising sufliciently to override the negative bias voltage on tube 23 of unit B and thus prevents tube 28 of unit B from ring. As track sections b and c fill up, tubes 2S of units C and D :are prevented from firing` With all tubes 2S non-conductive, all relays a', b', c', and d are deenergized.

It should be understood that While .four tra-ck sections are illustrated, the number of sections may be increased by making each section shorter. For example, with eight track sections and eight detector units instead of the four illustrated, liner control of railroad car speed is obtainable.

Retarder :control means 2 includes a computer 80, a control box 81 which receives a signal from computer 80, and a valve 82 which is seperated by control fbox 81 and which controls the amount of air pressure applied to retarder 1.

Computer 80, control box 81, valve 82, and retarder 1 are known terms of commercially available equipment obtainable from the Union Switch and Signal Division of Westinghouse Air Brake Company, Swlssvale, Pennsylvania, being components of that companys Type VR Automatic Retarder Control System which in turn is a part of Union Switch and Signals VELAC Automatic Classification Yard System. These components are illustrated in Union Switch and Signals Manual 527, dated November, 1957, entitled Installation and Maintenance Manual for Its Type VR Automatic Retarder System. Retarder valves, corresponding to valve 82 of the present application, are illustrated in FIG. 2(5) of Manual 527 entitled HS-1 Valve at Retarder and in FIG. 2(6) entitled X-l Valve at Retarder. A control box, corresponding to block 81 of the present application, appears in Manual 527 at FIG. 2(7) entitled Differential Pressure Unit at Retarder. Retarder plug-in units for the racks of the VELAC computer, corresponding to 'block off the present application, are illustrated in Manual 527 at an unnunrbered page in the rear portion of the manual, the illustrations being entitled Master Retarder Plug-in Unit :and Gnoup Retarder Plug-in Unit. FIG. 2(8) illustrates the Track Fullness Wheel Counter and FIG. 2(9) illustrates the Track Fullness Counters and Voltage Divider Racks employed by the prior-art Type VR Automatic Retarder Control System for counting the cars entering each classication track, such as track 11 of the present application, and transmitting a voltage signal into the electronic computer 80 proportionate to the number of cars counted.

In the prior-art apparatus, this voltage signal is based on the count of cars and assumed that as the number of cars on ya particular classicatiovn track, such las track 11, increased, the space available for following cars was reduced proportionately. The prior-art system, just rezferred to, works very satisfactorily provided each car rolls to approximately its intended destination on the classification track. However, if a car stops substantially short of its intended destination, the prior-art system has no means for adjusting for the error. For example, if the 15th car routed into the classication track stops Where the 35th car should stop, the prior-art system, Aby utilizing a car counter device, will merely indicate that lifteen cars are on the classification track and the next or 16th car will therefore be given an insutiicient amount of retarding tierce, and the 16th oar will crash into the 15th car with resulting damage to car and cargo.

The system of the present invention, unlike the priorart system, does not count the cars entering the classication track but instead detects the approximate location of each car, When stopped, or predicts the approximate stopping location of a car which is still moving when the following car enters the retarder. Thus, in the above example, if the th car stops short in the position which the 35th car should occupy, the system of the present invention will produce and deliver a voltage signal to the computer substantially identical to that which would have been produced and delivered when the 35th car reached its proper position. In other words, the system of the present application is arranged so that no distinction i-s made between thirty-five cars properly positioned on the classification track and fifteen cars on the classification track so spread tout las to occupy as much space vas thirty-five cars properly positioned. rllhus, the retarding force applied to each following car is suiiicient to :accomplish proper stopping, thereby avoiding the crashing impact which the prior-art system would have permitted.

Slow cut mechanism 4 is a safety device adapted to signal for the application of maximum retarding force when it senses that a car is rolling so slowly that the detecting system, comprising units A, B, C, and D, may not have time to perform its detecting function before the following car enters the track. Slow cut mechanism 4 is supplied with electrical power by a battery 83, land includes, Ain an electrical circuit, a iirst contact switch 84, a second contact switch 85, a quick-acting relay SC having a first armature 86 and a second armature S7, and a slow-acting repeater or follower relay SCP.

The circuit which is controlled by relay d of detector D, includes -a slow-acting repeater or follower relay DP having a first armature 88 and a second armature 39; the circuit which is controlled by relay c of detector C, includes a slow-acting follower relay CP which has a first armature 90 Iand a second armature 91; the circuit controlled =by relay b' of :detector B, includes a slow-acting follower relay BP which has a iirst armature 92 and a second armature 93; and the circuit controlled by control relay a of detector A includes slow-acting follower relay AP having a single armature.

Each of the slow-acting relays DP, CP, BP, and AP have a substantially different time delay, relay DP having the shortest delay, and relay AP the longest. For example, relay D-P may have a -second delay, relay CP -a 90- second delay, relay BP a 15G-second delay, and rel-ay AP a S60-second delay.

The operation and function of slow-cut mechanism 4 will first be described. Its purpose is to apply maximum retarding lforce to a car or cars which follow a slow car. In such case, the control 4system cannot afford to wait for the detector-controlled relay circuits to operate, since these circuits employ time-delay relays, as has just been mentioned, and `as will -be discussed in greater detail hereinbelow. Thus, slow-cut mechanism 4 is a safety device. Slow-cut mechanism Il is operatively positioned between the hump and the main entrance to the classification tracks. After the railroad car enters the classification tracks, the sensing mechanism 3 has control.

In oper-ation of slowacut mechanism 4, when the railroad vcar proceeds down the track, its wheels iirst strike contact switch 84 which momentarily opens. This deener-gizes fast-acting relay SC and opens its contacts at armatures 86 and 87. As the car proceeds, its wheels ynext strike contact switch SS and close it momentarily. This re-energizes the coil of relay SC and closes the contacts at armatures 86 and 87. If the car is traveling at a satisfactory speed, the time interval between lthe striking of first contact switch 84 and the striking of second contact switch 85 is such that slow-acting relay SCP does not have time to open. On the other hand, if the railroad car is traveling too slowly, relay SC remains de-energized long enough, and armature 87 remains open long enough, for relay SCP to de-energize, and its armature 6 drops to its lower contact. This sends a signal to computer which in turn sends a signal to retarder 1 which applies maximum braking on the following car.

The function of sensing mechanism 3, as already indicated, is to determine through detector units A, B, C, and D, whether track sections a, b, c, and d are empty or occupied by one or more railroad cars. U-nits A, B, C, and D control the associated control relays a', b', c', and d', respectively. When a railroad car enters track section d, all tubes 2S are biased into non-conduction and all of the control relays a', b', c', and d' are deenergized. The de-energizing of relay d opens the circuit of the coil of follower relay lDP. However, relay DP is a slow-release relay, and the armatures of relay DP remain in energized position for the period of its delay, assumed to be 2O seconds in the present example.

Assume that the car passes to track section c before expiration of the time-delay period of relay DP, i.e., before 2.0 seconds has elapsed. Exit of the car from section d causes tube 2S of unit D to fire and re-energizes relay d which closes the circuit of the coil of relay DP before the armatures of relay DP have had time to drop, as viewed in the drawing. However, the presence of the railroad car in track section c keeps tubes 28 of units C, B, Iand A biased off. Thus, relays c', b', and a remain de-energized. This keeps open the circuits to the coils of follower relays CP, BP, and AP. These relays are slow-release relays having longer time ldelays than relay DP and the armatures `of these relays remain in energized position for the periods of their respective delays.

Assume the car passes into track section b before expiration `of the time-delay period of relay CP, .assumed to be seconds in the present example. Exit of the car from section c causes the tube of unit C to fire and relay yc to .be re-energized, thus closing the circuit of the coil of relay CP before the -armatures of relay CP have had time to drop. The presence of the car on track section b keeps the tubes 2S of units B and A cut olf Vand the relays b and a rde-energized. This keeps open t-he circuits to the coils of follower lays BP and AP.

Assume the car passes into track section a before expiration of the time-delay period of relay BP, assumed to be seconds in the pre-sent example. Exit of the car from section b causes the relay b to be re-energized to re-establish the circuit including the coil of relay BP 'before the armatures of relay BP have dropped.

Assume the car stops in track section a. The entry of the railroad car into track 11 at entry 18 caused the time delay relay AP to `de-energize, and at the end of its timedelay period, assumed to be 360 seconds in the present example, the car still being in track section a, the relay AP operates and its armature drops. This completes the circuit of Ilamp 63a which is thereupon illuminated to signal the presence of the car in track section a. lt is to be noted that relay a .and follower relay AP Iare not connected in circuit with the retarder control means 2. This is because no braking signal is needed, no braking being applied from the retarder to the wheels of railroad cars which are destined for the most remote track section. Such cars need maximum speed, which for purposes of illustration, may be of the order of 1l miles per hour.

Whether or not track section a is filled up, if a car stops in track section b, the tube 28 of -unit B remains biased off and control relay b remains open. Slow-acting follower relay BP, at the end of its time delay (of 150 seconds), drops armatures 92 and 93. r[he circuit which is completed through armature 92 is effective to illuminate lamp 68b and the circuit completed through armature 93 is effective to 4send a signal back to computer 80 which is translated and applied to retarder 1 to adjust the amount of braking applied to the wheels of succeeding railroad cars.

lt will be seen `from the foregoing description that when no car is on the track 1l, all four tubes 28 are conducting and all fofur relays DP, CP, BP, and AP are energized, their armatures being in the positions shown in the draw-l ing. When la car iirst enters classification track 11, all primary windings 25 are substantially shorted and all tubes 28 become Ibiased into non-conduction. Thus, all four relays DP, CP, BP, and AP are de-energized.

Thereafter, as the car passes through track sections d, c, and b, in that order, on its way to track section a, tubes 28 in units D, C, and B again conduct and only the tube in unit A remains extinguished. Time-delay relay AP, after lbeing in `(le-energized condition for the period of its time delay, 360 seconds, drops its armature, and a connection is made which illuminates lamp 68a.

As each additional car enters and proceeds along track 11 at a satisfactory speed, the action described above is repeated until a car stops in track section b. When this occurs, the voltage across the rails 12, 13 of track 11 at entry point 18 is held ydown to such a value that tube 28 in unit B is no longer Ibiased to conduct, and it cuts oli. Thus time-delay rel-ay BP is not re-energized and at the expiration of its time-delay period, it drops its armatures.

Prior to relay BP dropping its armatures, a circuit had existed iirom the positive terminal of battery 83 through the armature of relay SCP and the lower armatures of relays DP, CP, and BP in the up position, Ito computer 80 via conductor a, andthen back to the negative terminal of battery 83. While not shown in the drawing, computer 80 may be assumed to include a voltage divider type of network having a fixed pick oit output connection at a low point on the network; and the conductor a may be assumed to be connected to the network at a fixed point albove the pick off. '[lhus, the voltage picked olf is a fraction of the total battery voltage, for example, onehalf of the battery voltage.

When the Atube of unit B cuts oli and relay BP, at the expiration of its time-delay period, drops its armatures, the positive terminal of battery 83 becomes connected to computer y80 via armature 93 in its down position and conductor b". Conductor b may be assumed connected to the computers voltage divider network at a higher point than conductor a". Thus, the voltage now picked oft is lower, for example, oneathird of the battery voltage.

In similar manner, after track section b has become filled with cars and a car stops for the iirst time in section c, the voltage across the rails of track 11 at entry point 18 is no longer high enough to keep tube 28 in unit C ybiased to conduct and this tube becomes extinguished. When that occurs, relay CP is not re-energized and, at the expiration of its time-delay period, it drops its 'armatures. A voltage from battery 83 is now applied to the computer 80 through the lower armature 91 of relay CP in its down position and conductor c". Conductor c may be assumed to be connected to a higher point on the computer voltage divider network than either of conduotors a or b" and, accordingly, a still lower voltage is derived `from the iixed pick ofi, for exam-ple, onequarter of the 'battery Voltage.

Finally, track section c lls up and a car stops in track section d. The voltage across the rails of -track 11 at entry point 18 is now so low that tube 28 in unit D becomes non-conducting and time-delay relay DP, being in rde-energized condition, drops its armature at the expiration of its time-delay period. At that time, the positive terminal of 'battery 83 is connected to the computer voltage divider network through the lower armature 89' of relay DP and conductor d". Conductor d" may tbe assumed to be connected to a still higher point on Jthe voltage divider network of the computer, and a voltage is derived at the xed pick off which is. still lower, for example, one-iith of the battery voltage.

The voltage derived from .the computer voltage divider network is thus dependent on the condition of relays DP, CP, and B-P. This derived voltage controls the application of a Avoltage to the control box 81 to control the air pressure released by valve 82 which in turn controls the amount of retarding force applied to the wheels of a succeeding car based on information sensed as to the approximate stopping position of a preceding car.

The automatic retarder system described and claimed in the present application has recently been placed into operation in the Conway classification yard of the Pennsylvania Railroad where it functions as a component of the complex classication system there in operation.

The automatic retarder system of the present application may be summarized as follows: The track 11 may be looked upon as divided into a plurality of approximate sections defined by track voltage levels. No physical means defines these sections; they are electrically dened and are approximate only. The sections are illustrated as of approximately the same length, but in practice the sections nearer to the entry point 1-8 would be shorter since the cars are moving faster in these sections and more control is desired in order to give greater protection against a collision involving a fast moving car.

It was stated previously herein that when a car is at the track entrance, indicated in the drawing by the dotted line 18, the voltage across the track is reduced to substantially zero due to the shunting action of the car and that as the car moves along the track, the track voltage at entrance point 18 starts to rise. When the car reaches a point represented by dotted line 17, the track voltage at the track entrance 18 was said to have risen to, for example, 0.5 volt. Line 17 is thus arbitrarily and electrically dened as the limit of track section d. When the car reaches a point represented by dotted line 16, the track voltage at track entrance 18 has risen to, for example, 1.10 volt. This is the arbitrarily and electrically defined limit of track section c. When the car reaches a point represented by the dotted line 15, the track voltage at the entrance 18 is, for example, l1.5 volts. This defines the l'imit of track section b. And when the car reaches a point represented by dotted line 14, the track voltage at entrance point -18 is, for example, 2.11 volts.

As also described previously, the voltage-sensitive circuits A, B, C, and D are so biased that when the track Y voltage at entrance .18 s zero volts, all of the tubes 28 are cut oit. When the track voltage at point 18 rises to 0.5 volt, fthe tube 28- in D section lires. When the track voltage at point 18 rises to 1.0 volt, the tube 28 in section C fires. When the track voltage at point 18 rises to 1.5 volts, tube 28- in section B fires. And when the track voltage at point 18 rises to 2.1 `volts, tube 28 in circuit A res.

Each of the four time-delay relays DP, CP, BP, and AP is associated with a corresponding one of the four voltagesensitive circuits D, C, B, and A. Each of the tour timedelay relays :is a slow-break relay, and each is set to break a different length of time following de-energization. For illustration, it was assumed that relay DP was set to have a time delay of 2.0 seconds, relay CP a delay of seconds, relay BP a delay of seconds, and relay AP a delay of 360 seconds.

Relay DP having the shortest delay is coupled to and controlled by voltage-sensitive circuit D which :is the first to lire. Relay CP having the next shortest delay is coupled to and controlled by voltage-sensitive circuit C which (is the second circuit to fire. Relay BP having the third shortest delay is coupled to and controlled by voltagesensitive circuit B which is the third circuit to fire. And relay AP Ihaving the longest time delay is associated with voltage-sensitive circuit A which is the last circuit to re.

In the event that more than one of the relays DP, CP, and BP operates, that is, drops its armatures at the end of its time-delay period, then the operated relay having the shortest time del-ay controls; and such operated relay controls the application of the greater retarding force to the car next to pass through the retarder. For example, if both of the relays lCP and BP have operated, i.e., have dropped their armatures but relay DP has not, then the relay CP controls. This is evident -from the circuit of the drawing which shows that with armature 91 of relay CP in the dropped position, the relay BP is cut out of the circuit and the circuit to the conductors b and a" is open. Thus, conductor c controls the retarder. However, if relay `DP has also operated, then relay CP is cut out of the circuit at the open contact of armature 89 in the dropped position, and the circuit to conductors c", b", and a" is open. Thus, conductor d controls the retarder. It will be seen then that the operated relay having the shortest time delay controls the retarder.

Relays capable of providing the lengths of delay indicated above are available commercially. One example is the Agastat, which is the trade name of a series of timedelay relays made by the Elastic Stop Nut Corportation. These relays are capable of time delays up to minutes. They operate pneumatically. Such relays are described in U.S. Patent 2,627,919, issued lFebruary 10, 1953, and assigned to Elastic Stop Nut Corporation.

ln the automatic retarder control system described and claimed herein, if all cars move `along track il at satisfactory speeds, the relays AP, BP, CP, and DP will operate (i.e., drop their armatures) in the order just named. Relay AP will operate iirst. Relay BP will not operate until section a is filled and a car stops short of 4line Il5; relay CP will not operate until section b is iilled and a car stops short of line 16; and relay DP will not operate until section c is filled and 'a car stops short of line 17. However, if all cars do not move along at satisfactory speeds, the order in which the relays AP, BP, CP, and DP operate will depend on the particular situation. For example, if the first car to move along at less than satisfactory speed came along before section a had filled up, and if its speed was suiciently slow so that the car was still in section d when the time delay of relay DP expired (20 seconds in the present example) then relay DP would operate. Thereafter, relay CP would operate, since the said slow car, if it cleared section d at all, would stop in section c. However, the operation of relay CP would have no effect, since relay DP had already operated. And, as previously described, as between two operated relays, the relay having the shorter time delay controls.

If we assume that, before section a had iilled with cars, the first slow car to come along cleared section d in time but failed to clear section c in time, fthen relay CP would operate, and thereafter relay BP would operate since the car, if it cleared section c at all, would stop in section b. ln such case, relay CP would control the retarder, and relay BP would have no effect.

It will be understood that the time delays for the relays DP, CP, and BP are so chosen that the only cars which do not move through the particular track section in time are those which are moving so slowly that they will either stop in the section or -will roll but a short distance beyond the particular track section before coming to a complete stop. Thus, =a car which does not move through track section d within 20 seconds will come to a complete stop either in section d or shortly after crossing into section c; and la car which clears section d in time but does not clear section c Within 9() seconds will come to a complete stop either in section c or early in section b.

While the preferred embodiment of this invention has been described in some detail, it will be obvious to one skilled in the art that various modifications may be made without departing from the invention as hereinafter claimed.

Having described our invention, we claim:

l. In a railroad car retarder system having retarder means disposed along a track and adapted to apply different amounts of retarding yforce to a passing railroad car according to the different control signals applied thereto; voltage generator means connected across the track at a control point located near to said retarder means, said voltage generator means being characterized by having poor voltage regulation; a plurality of voltage-sensitive switching means connected in parallel across said track at said control point for sensing the track voltage yat said point; a plurality of time-delay relays, one controlled by each of said voltage-sensitive switching means, each of said time-delay relays being set to operate at the expiration of a different time period following deenergization, each of said voltage-sensitive switching means being operative to `cie-energize its associated timedelay relay at the low track-voltage level which exists at said control point when a railroad car shunts the track at said control point, each of said voltage-sensitive switching means being biased differently land operative to reenergize its associated relay aat a different track-voltage level a-t said control point, whereby each time-delay operyates only in `the event said relay is not re-energized during its time-delay period; and means for applying to said retarder means a control signal controlled by that one of the time-delay relays which has operated and which also has the shortest time delay.

2. In a railroad car retarder system: a track comprising :a pair of rails extending lengthwise and having a point of entrance for cars, said rails being continuous electrically; retarder means disposed to apply a controllable amount of retarding -iorce to la car rolling toward said point of entrance; and control means for controlling automatically the amount of retarding force appl-led as a function of the movement of a preceding car, said control means comprising: a voltage generator having poor voltage regulation connected across said track at the point :of entrance; a plural-ity of voltage-sensitive switching circuits connected in parallel across lthe track ait the point of entrance; means for adjusting each of said voltage-sensitive switching circuits to open at the low voltage level which exists when a car shunts the rails at said point of entrance and to close at a different higher voltage level; a plurality of time-delay relays, one each coupled to and controlled by each of said voltage-sensitive switching circuits, each of said time-delay relays being set to operate at the expiration of a different period of time following its de-energization unless re-energized during that period by the closing of its associated voltagesensitive switching circuit, the time-delay relay set to have the shortest delay period being coupled to and controlled by the ivoltage-sensitive switching circuit adjusted to close 'at the lowest of said higher voltage levels, the time-delay relay set to have the second shortest delay period being coupled to ,and controlled by the voltagesensitive switching circuit adjusted to close at the second lowest of said higher voltage levels, etc.; and means for controlling said retarder means by the time-delay relay which has operated and which also has the shortest timedelay period.

3. In a railroad classification yard system having a plurality of tracks each consisting of a pair of spacedapart rails insulated electrically from the remainder of the yard system, each rail comprising a plurality of rail sections electrically connected together in end-to-end fashion; retarder means disposed at the track entrance and adapted to apply a controllable variable retarding force to a passing car according to a control signal applied; retarder control means for applying a control signal to said retarder means; relay means for controlling said retarder control means, said relay means comprising a plurality of time-delay slow-release relays each set to release at the expiration of a different delay period following de-energization; a voltage generator of poor voltage regulation connected across the track entrance; a plurality of voltage-sensitive switching means coupled in parallel across the track entrance; means coupling each of said voltage-sensitive switching means to a different one of said time-delay relays for controlling said relays; means biasing each of said voltage-sensitive switching means diiierently, said voltage-sensitive switching means being adapted, in response to the drop in voltage across the track section when a car lirst enters the track, to de-energize each of the time-delay relays, each of said Voltage-sensing switching means being adapted to be triggered on at a progressively diierent time in response to the rise in voltage across said track entrance as the car moves farther along the track away from the track entrance, each of said time'delay relays being set to withhold release of its contacts for a different period of time following deenergization, said period of time corresponding in each case to that required by a car moving at a satisfactory selected speed to move along a portion of the track; and means coupling said relay means to said retarder control means to so control said retarder means as to apply the greatest retarding force when the relay having the shortest release time is not re-energized prior to the expiration of its time-delay period and to apply the least retarding force when all of the time-delay relays except the one having the slowest release time are re-energized prior to the expiration of their respective time-delay periods.

4. In a railroad classification `yard system having a plurality of tracks each consisting of a pair of spacedapart rails insulated electrically from the remainder of the yard system, each rail comprising a plurality of rail` sections electrically connected together in end-to-end fashion; retarder means associated with said track and disposed near the track entrance; retarder control means to control the retarding force exerted by said retarder means; an electric generator having poor voltage regulation connected across the track entrance; a plurality of as said car moves progressively along said track raising progressively the track voltage at the track entrance; a plurality of time-delay relays, one controlled by each of said sensing circuits, each of said relays being set to operate after a different time delay after de-energizing, the

relay controlled by the particular sensing circuit which is biased to be triggered on irst being set to operate after vthe shortest time delay and the relay controlled by the sensing circuit biased to be triggered on last being set to operate after the longest time delay, switching means vcoupling each of said relays to its particular sensing circuit and adapted to open the relay circuit to de-energize the relay when its associated sensing circuit is turned off and to re-energize said time-delay relay when said sensing circuit is turned on; and means for controlling said retarder control means by that relay which has operated and has the shortest time delay.

No references cited. 

1. IN A RAILROAD CAR RETARDER SYSTEM HAVING RETARDER MEANS DISPOSED ALONG A TRACK AND ADAPTED TO APPLY DIFFERENT AMOUNTS OF RETARDING FORCE TO A PASSING RAILROAD CAR ACCORDING TO THE DIFFERENT CONTROL SIGNALS APPLIED THERETO; VOLTAGE GENERATOR MEANS CONNECTED ACROSS THE TRACK AT A CONTROL POINT LOCATED NEAR TO SAID RETARDER MEANS, SAID VOLTAGE GENERATOR MEANS BEING CHARACTERIZED BY HAVING POOR VOLTAGE REGULATION; A PLURALITY OF VOLTAGE-SENSITIVE SWITCHING MEANS CONNECTED IN PARALLEL ACROSS SAID TRACK AT SAID CONTROL POINT FOR SENSING THE TRACK VOLTAGE AT SAID POINT; A PLURALITY OF TIME-DELAY RELAYS, ONE CONTROLLED BY EACH OF SAID VOLTAGE-SENSITIVE SWITCHING MEANS, EACH OF SAID TIME-DELAY RELAYS BEING SET TO OPERATE AT THE EXPIRATION OF A DIFFERENT TIME PERIOD FOLLOWING DE- 